Oleanolic acid is known to possess beneficial effects on the regulation of the cardiovascular homeostasis. However, the exact nature of the role of oleanolic acid on the regulation of body fluid balance and blood pressure homeostasis and its mechanisms involved are not well defined. Experiments were performed to identify the effects of oleanolic acid on the renin-angiotensin system and cardiac natriuretic hormone (ANP) system, and also renal function and blood pressure in normotensive and renovascular hypertensive rats. The change in the plasma levels of hormones and the expressions of renin, angiotensin II receptors, ANP, natriuretic peptide receptor-C, M2 muscarinic receptor and GIRK4 were determined in the kidney, heart and aorta. Oleanolic acid was administered orally for 1 or 3 weeks. Here, we found that oleanolic acid suppressed plasma levels of renin activity and aldosterone and intrarenal levels of renin and angiotensin II type 1 receptor expression and increased angiotensin II type 2 receptor in normotensive and hypertensive rats. Also, oleanolic acid increased plasma levels of ANP. Further, oleanolic acid suppressed angiotensin II type 1 receptor and natriuretic peptide receptor-C expression and increased angiotensin II type 2 receptor and ANP expression in the heart and aorta. Along with these changes, oleanolic acid accentuated urinary volume, electrolyte excretion and glomerular filtration rate in normotensive rats and suppressed arterial blood pressure in hypertensive rats. These findings suggest that beneficial effects of oleanolic acid on the cardiorenal system are closely associated with its roles on the renin-angiotensin system and cardiac natriuretic hormone system.